Re: nmi_watchdog=2 regression in 2.6.21

[Stephane Eranian <eranian@hpl.hp.com>]

[-- Attachment #1: Type: text/plain, Size: 1013 bytes --]

Daniel,

On Wed, Aug 29, 2007 at 06:21:59PM -0700, Daniel Walker wrote:
> On Wed, 2007-08-29 at 14:24 -0700, Stephane Eranian wrote:
> 
> 
> > Now on Core Duo, there is no PEBS anyway, so it is okay to use counter 0
> > for NMI. The problem is that the detection code in perfctr-watchdog.c
> > treats a Core Duo and a Core 2 Duo the same way as they both have the
> > X86_FEATURE_ARCH_PERFMON bit set.
> > 
> > I have attached a patch with handle the case of the Core Duo. Unfortunately,
> > I do not own one so I cannot test it. I would appreciate if you could
> > try re-applying my counter 0 -> 1 patch + this new one to see if you
> > have the problem with the NMI getting stuck.
> 
> I tested your patch .. The system doesn't hang, but the NMI seems to
> disappear .. The check_nmi_watchdog() is not called, and the NMI never
> actually starts firing .. Is that what you had intended?
> 
Yes, I realized I missed a small detail in the switch statement.
Could you try the new version?

Thanks.

-- 
-Stephane

[-- Attachment #2: coreduo.diff --]
[-- Type: text/plain, Size: 1246 bytes --]

diff --git a/arch/i386/kernel/cpu/perfctr-watchdog.c b/arch/i386/kernel/cpu/perfctr-watchdog.c
index 9b5d6af..3a945f0 100644
--- a/arch/i386/kernel/cpu/perfctr-watchdog.c
+++ b/arch/i386/kernel/cpu/perfctr-watchdog.c
@@ -613,6 +613,17 @@ static struct wd_ops intel_arch_wd_ops = {
 	.evntsel = MSR_ARCH_PERFMON_EVENTSEL1,
 };
 
+/*
+ * Check for Intel Core Duo because it has a bug with PERFEVTSEL1
+ * (see Spefication Update bug AE49) and must use PERFEVTSEL0. We cannot
+ * use this counter on other processors supporting X86_FEATURE_ARCH_PERFMON
+ * because PEBS requires it.
+ */
+static inline int is_coreduo(void)
+{
+	return boot_cpu_data.x86 == 6 && boot_cpu_data.x86_model == 14;
+}
+
 static void probe_nmi_watchdog(void)
 {
 	switch (boot_cpu_data.x86_vendor) {
@@ -623,13 +634,14 @@ static void probe_nmi_watchdog(void)
 		wd_ops = &k7_wd_ops;
 		break;
 	case X86_VENDOR_INTEL:
-		if (cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON)) {
+		if (cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON)
+		    && !is_coreduo()) {
 			wd_ops = &intel_arch_wd_ops;
 			break;
 		}
 		switch (boot_cpu_data.x86) {
 		case 6:
-			if (boot_cpu_data.x86_model > 0xd)
+			if (boot_cpu_data.x86_model > 0xe)
 				return;
 
 			wd_ops = &p6_wd_ops;